Image sensor with reduced optical path

ABSTRACT

Among other things, one or more image sensors and techniques for forming image sensors are provided. An image sensor comprises a photodiode array configured to detect light. The image sensor comprises an oxide grid comprising a first oxide grid portion and a second oxide grid portion. A metal grid is formed between the first oxide grid portion and the second oxide grid portion. The oxide grid and the metal grid define a filler grid. The filler grid comprises a filler grid portion, such as a color filter, that allows light to propagate through the filler grid portion to an underlying photodiode. The oxide grid and the metal grid confine or channel the light within the filler grid portion. The oxide grid and the metal grid are formed such that the filler grid provides a relatively shorter propagation path for the light, which improves light detection performance of the image sensor.

RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S. patent application Ser. No. 15/244,355, titled “IMAGE SENSOR WITH REDUCED OPTICAL PATH” and filed on Aug. 23, 2016, which claims priority to U.S. patent application Ser. No. 14/100,598, titled “IMAGE SENSOR WITH REDUCED OPTICAL PATH” and filed on Dec. 9, 2013, which is a Non-Provisional filing of U.S. Patent Application 61/910,165, titled “IMAGE SENSOR WITH REDUCED OPTICAL PATH” and filed on Nov. 29, 2013. U.S. patent application Ser. Nos. 15/244,355, 14/100,598, and 61/910,165 are incorporated herein by reference.

BACKGROUND

An image sensor is a type of semiconductor device that converts an optical input into an electrical signal. The image sensor comprises an array of light detecting elements, such as photodiodes, where a light detecting element is configured to produce an electrical signal corresponding to an intensity of light impinging on the light detecting element. The electrical signal is used, in some instances, to display an image corresponding to the optical input.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a method of forming an image sensor, according to some embodiments.

FIG. 2 is an illustration of a photodiode array of an image sensor, according to some embodiments.

FIG. 3 is an illustration of a first oxide layer of an image sensor, according to some embodiments.

FIG. 4 is an illustration of a metal layer of an image sensor, according to some embodiments.

FIG. 5 is an illustration of a second oxide layer of an image sensor, according to some embodiments.

FIG. 6 is an illustration of defining an oxide grid and a metal grid of an image sensor, according to some embodiments.

FIG. 7 is an illustration of a capping layer of an image sensor, according to some embodiments.

FIG. 8 is an illustration of an image sensor detecting light, according to some embodiments.

FIG. 9 is a flow diagram illustrating a method of forming an image sensor, according to some embodiments.

FIG. 10 is an illustration of a photodiode array of an image sensor, according to some embodiments.

FIG. 11 is an illustration of a first oxide layer of an image sensor, according to some embodiments.

FIG. 12 is an illustration of a metal layer of an image sensor, according to some embodiments.

FIG. 13 is an illustration of defining a metal grid of an image sensor, according to some embodiments.

FIG. 14 is an illustration of a capping layer and a second oxide layer of an image sensor, according to some embodiments.

FIG. 15 is an illustration of defining an oxide grid of an image sensor, according to some embodiments.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to the drawings, wherein like reference numerals are generally used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide an understanding of the claimed subject matter. It is evident, however, that the claimed subject matter can be practiced without these specific details. In other instances, structures and devices are illustrated in block diagram form in order to facilitate describing the claimed subject matter.

One or more image sensors and techniques for forming such image sensors are provided herein. According to some embodiments, an image sensor comprises a photodiode array formed over or within a substrate. The photodiode array comprises one or more photodiodes, such as image sensor pixels, configured to accumulate energy generated by light, such as from photons, of an optical input. A voltage of a photodiode is read as an output for the optical image. In some embodiments, a photodiode is situated under one or more layers or components formed over the substrate. Because light travels along a light propagation path that comprises such layers or components before reaching the photodiode, signal strength of the light can decay before reaching the photodiode or the light can travel towards another photodiode that is not to detect the light. Accordingly, as provided herein, an oxide grid portion and a metal grid portion, defining a filler grid that channels light towards photodiodes, are formed such that a light propagation path is reduced. Reducing the light propagation path improves performance of the image sensor, such as improving a signal to noise ratio for the image sensor or improving color detection by the image sensor. The light propagation path is reduced because the filler grid is defined as being substantially between a top surface of a first oxide grid portion of the oxide grid and a top surface of a second oxide grid portion of the oxide grid.

A method 100 of forming an image sensor, according to some embodiments, is illustrated in FIG. 1, and one or more image sensors formed by such a methodology are illustrated in FIGS. 2-8. An image sensor 200 comprises a photodiode array 210 formed within a substrate 202, as illustrated in FIG. 2. In some embodiments, the photodiode array 210 comprises a first photodiode 204, a second photodiode 206, a third photodiode 208, or other photodiodes configured to detected light. At 102, a first oxide layer 302 is formed over the photodiode array 210 as a first oxide grid portion 302 a of an oxide grid, as illustrated in FIG. 3. In some embodiments, the first oxide layer 302 has a height between about 500A to about 3000A. In some embodiments, the first oxide layer 302 is formed by a deposition process.

At 104, a metal layer 402 is formed over the first oxide layer 302, as illustrated in FIG. 4. In some embodiments, the metal layer 402 has a height between about 1000A and about 3000A. In some embodiments, the metal layer 402 has a width between about 0.1 microns and about 0.2 microns. In some embodiments, the metal layer 402 is formed by a film deposition process.

At 106, a second oxide layer 502 is formed over the metal layer 402, as illustrated in FIG. 5. In some embodiments, the second oxide layer 502 has a height between about 200A to about 5000A. In some embodiments, the second oxide layer 502 is formed by a deposition process. In some embodiments, a chemical mechanical polishing (CMP) process is performed after deposition of the second oxide layer 502.

At 108, an etch 600 is performed through the second oxide layer 502 and through the metal layer 402 to form a metal grid 402 a and to form a second oxide grid portion 502 a of the oxide grid, as illustrated in FIG. 6. The second oxide grid portion 502 a is formed over the metal grid 402 a. The second oxide grid portion 502 a and the metal grid 402 a define a filler grid 602 within which a fill material, such as a color filter material that guides light towards the photodiode array 210, could be formed. The filler grid is formed substantially between a top surface 604 of the first oxide grid portion 302 a and a top surface 606 of the second oxide grid portion 502 a. In some embodiments, a bottom surface of the filler grid 602 is formed below the second oxide grid portion 502 a. In some embodiments, the bottom surface of the filler grid 602 is formed below a top surface 608 of the metal grid 402 a.

In some embodiments, the filler grid 602 comprises a first filler grid structure 610 formed between a first metal grid structure 612 of the metal grid 402 a and a second metal grid structure 614 of the metal grid 402 a. In some embodiments, the first filler grid structure 610 is formed between a first oxide grid structure 616 of the second oxide grid portion 502 a and a second oxide grid structure 618 of the second oxide grid portion 502 a. In some embodiments, the first filler grid structure 610 is confined on a first side by the first oxide grid structure 616 and the first metal grid structure 612. The first filler grid structure 610 is confined on a second side by the second oxide grid structure 618 and the second metal grid structure 614. The first filler grid structure 610 is confined on a bottom side by the first oxide grid portion 302 a.

In some embodiments, a capping layer 702 is formed to line the filler grid 602, as illustrated in FIG. 7. In some embodiments, the capping layer 702 comprises a material, such as an oxide film, used to protect the metal grid 402 a, such as from moisture issues resulting from a fill material used to fill the filler grid 602. In some embodiments, the capping layer 702 is formed using a conformal oxide deposition process. In some embodiments, the capping layer 702 has a thickness between about 200A to about 1500A. In some embodiments, the capping layer 702 is formed between the filler grid 602 and the first oxide grid portion 302 a. In some embodiments, the capping layer 702 is formed between the filler grid 602 and the metal grid 402 a. In some embodiments, the capping layer 702 is formed between the filler grid 602 and the second oxide grid portion 502 a.

FIG. 8 illustrates the second photodiode 206 of the image sensor 200 detecting light 808. The image sensor 200 comprises one or more lens structures, such as a first lens structure 802, a second lens structure 804, and a second lens structure 806. In some embodiments, light 808, incident to the second lens structure 804, is focused towards the first filler grid structure 610 comprises a color filter material. The color filter material of the first filler grid structure 610 allows at least some of the light 808 to propagate towards the second photodiode 206. At least one of the first oxide grid portion 302 a of the oxide grid, the second oxide grid portion 502 a of the oxide grid, or the metal grid 402 a confines the light 808 so that the light is detected by the photodiode 206 as opposed to being detected by a different photodiode that is not to detect the light 808. Because the first filler grid structure 610 is confined by the oxide grid and the metal grid 402 a, such as being formed between the top surface 606 of the second oxide grid portion 502 a and the top surface 604 of the first oxide grid portion 302 a as illustrated in FIG. 6, a light propagation path for the light 808 is reduced. Reducing the light propagation path improves performance of the image sensor 200, such as improved detection of the light 808 by the second photodiode 206.

A method 900 of forming an image sensor, according to some embodiments, is illustrated in FIG. 9, and one or more image sensors formed by such a methodology are illustrated in FIGS. 10-15. An image sensor 1000 comprises the photodiode array 210, comprising the first photodiode 204, the second photodiode 206, and the third photodiode 208, formed within the substrate 202, as illustrated in FIG. 10. At 902, the first oxide layer 302 is formed over the photodiode array 210 as the first oxide grid portion 302 a of the oxide grid, as illustrated in FIG. 11. At 904, the metal layer 402 is formed over the first oxide layer 302, as illustrated in FIG. 12. At 906, a first etch 1300 is performed through the metal layer 402 to form the metal grid 402 a. In some embodiments of performing the first etch 1300, a hard mask is formed over the metal layer 402, such that a portion of the hard mark overlays a portion of the metal layer 402 to define the metal grid 402 a during the first etch 1300.

In some embodiments, a capping layer 1400 is formed over the metal grid 402 a, as illustrated in FIG. 14. In some embodiments, the capping layer 1400 has a thickness between about 100A to about 2000A. In some embodiments, the capping layer 1400 comprises a nitride material or an oxide material. At 908, a second oxide layer 502 is formed over the metal grid 402 a, as illustrated in FIG. 14. In some embodiments, the second oxide layer 502 is formed over the capping layer 1400. In some embodiments, a CMP process is performed on the second oxide layer 502. At 910, a second etch 1500 is performed through the second oxide layer 502 to form the second oxide grid portion 502 a of the oxide grid, as illustrated in FIG. 15. At least one of the oxide grid, such as the first oxide grid portion 302 a and the second oxide grid portion 502 a, or the metal grid 402 a define the filler grid 602. In this way, the filler grid 602 is formed according to a multiple etch process.

According to an aspect of the instant disclosure, an image sensor is provided. The image sensor comprises a photodiode array formed over a substrate. The image sensor comprises a first oxide grid portion of an oxide grid. The first oxide grid portion is formed over the photodiode array. The image sensor comprises a metal grid that is formed over the first oxide grid portion. The image sensor comprises a second oxide grid portion that is formed over the metal grid. The image sensor comprises a filler grid that is formed substantially between a top surface of the first oxide grid portion and a top surface of the second oxide grid portion.

According to an aspect of the instant disclosure, a method for forming an image sensor is provided. The method comprises forming a first oxide layer over a photodiode array comprised within a substrate. The first oxide layer is formed as a first oxide grid portion of an oxide grid. A metal layer is formed over the first oxide layer. An etch is performed through the second oxide layer and the metal layer to form a metal grid and to form a second oxide grid portion of the oxide grid. The oxide grid and the metal grid define a filler grid formed substantially between a top surface of the first oxide grid portion and a top surface of the second oxide grid portion.

According to an aspect of the instant disclosure, a method for forming an image sensor is provided. The method comprises forming a first oxide layer over a photodiode array comprised within a substrate. The first oxide layer is formed as a first oxide grid portion of an oxide grid. A metal layer is formed over the first oxide layer. A first etch is performed through the metal layer to form a metal grid. A second oxide layer is formed over the metal grid. A second etch is performed through the second oxide layer to form a second oxide grid portion of the oxide grid. The oxide grid and the metal grid define a filler grid formed substantially between a top surface of the first oxide grid portion and a top surface of the second oxide grid portion.

Although the subject matter has been described in language specific to structural features or methodological acts, it is to be understood that the subject matter of the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as embodiment forms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order in which some or all of the operations are described should not be construed to imply that these operations are necessarily order dependent. Alternative ordering will be appreciated given the benefit of this description. Further, it will be understood that not all operations are necessarily present in each embodiment provided herein. Also, it will be understood that not all operations are necessary in some embodiments.

It will be appreciated that layers, features, elements, etc. depicted herein are illustrated with particular dimensions relative to one another, such as structural dimensions or orientations, for example, for purposes of simplicity and ease of understanding and that actual dimensions of the same differ substantially from that illustrated herein, in some embodiments. Additionally, a variety of techniques exist for forming the layers features, elements, etc. mentioned herein, such as etching techniques, implanting techniques, doping techniques, spin-on techniques, sputtering techniques such as magnetron or ion beam sputtering, growth techniques, such as thermal growth or deposition techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma enhanced chemical vapor deposition (PECVD), or atomic layer deposition (ALD), for example.

Further, unless specified otherwise, “first,” “second,” or the like are not intended to imply a temporal aspect, a spatial aspect, an ordering, etc. Rather, such terms are merely used as identifiers, names, etc. for features, elements, items, etc. For example, a first channel and a second channel generally correspond to channel A and channel B or two different or two identical channels or the same channel.

Moreover, “exemplary” is used herein to mean serving as an example, instance, illustration, etc., and not necessarily as advantageous. As used in this application, “or” is intended to mean an inclusive “or” rather than an exclusive “or”. In addition, “a” and “an” as used in this application are generally to be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. Also, at least one of A and B or the like generally means A or B or both A and B. Furthermore, to the extent that “includes”, “having”, “has”, “with”, or variants thereof are used, such terms are intended to be inclusive in a manner similar to “comprising”.

Also, although the disclosure has been shown and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the annexed drawings. The disclosure includes all such modifications and alterations and is limited only by the scope of the following claims. In particular regard to the various functions performed by the above described components (e.g., elements, resources, etc.), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure. In addition, while a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. 

What is claimed is:
 1. A method for forming an image sensor, comprising: forming a photodiode array within a substrate; forming a metal layer over the photodiode array; etching the metal layer to define a first trench overlying a first photodiode of the photodiode array; forming a capping layer in the first trench and over the metal layer; forming a first oxide layer over the capping layer; and etching the first oxide layer to define a second trench over the first trench, wherein etching the first oxide layer comprises exposing the capping layer.
 2. The method of claim 1, comprising: forming a color filler material in the second trench, wherein the color filler material is configured to filter wavelengths within a defined range of wavelengths.
 3. The method of claim 2, wherein the color filler material is in contact with a sidewall of the first oxide layer and a sidewall of the capping layer.
 4. The method of claim 1, comprising: forming a second oxide layer over the photodiode array and the substrate prior to forming the metal layer.
 5. The method of claim 4, comprising: etching the second oxide layer, wherein the first trench is further defined by the second oxide layer.
 6. The method of claim 5, wherein a sidewall of the metal layer and a sidewall of the second oxide layer together define a sidewall of the first trench, and an upper surface of the second oxide layer defines a bottom of the first trench.
 7. The method of claim 4, wherein etching the metal layer to define the first trench comprises: exposing the second oxide layer.
 8. The method of claim 1, wherein the capping layer contacts a top surface of the metal layer and a sidewall of the metal layer.
 9. The method of claim 8, comprising: forming a second oxide layer over the photodiode array and the substrate prior to forming the metal layer, wherein: etching the metal layer to define the first trench comprises exposing a first portion of the second oxide layer, and the capping layer is in contact with the first portion of the second oxide layer.
 10. A method for forming an image sensor, comprising: forming a photodiode array within a substrate; forming a metal layer over the photodiode array; forming a first oxide layer over the metal layer; etching the first oxide layer to define a trench overlying a first photodiode of the photodiode array; and forming a capping layer in the trench.
 11. The method of claim 10, comprising: forming a second oxide layer over the photodiode array and the substrate prior to forming the metal layer.
 12. The method of claim 11, comprising: etching the metal layer to expose the second oxide layer, wherein the trench is further defined by the metal layer and the second oxide layer.
 13. The method of claim 12, wherein the capping layer is in contact with the first oxide layer, the metal layer, and the second oxide layer.
 14. The method of claim 11, comprising: forming a color filler material in the trench, wherein: the color filler material is configured to filter wavelengths within a defined range of wavelengths, and the color filler material is separated from the first photodiode by the capping layer and the second oxide layer.
 15. The method of claim 10, comprising: forming a color filler material in the trench, wherein the color filler material is configured to filter wavelengths within a defined range of wavelengths.
 16. The method of claim 15, wherein the color filler material is separated from the first oxide layer by the capping layer.
 17. The method of claim 15, wherein the color filler material is separated from the metal layer by the capping layer.
 18. A method for forming an image sensor, comprising: forming a photodiode array within a substrate; forming a first oxide layer over the substrate; forming a metal layer over the first oxide layer; etching the metal layer and the first oxide layer to define a first trench overlying a first photodiode of the photodiode array; forming a capping layer in the first trench and over the metal layer, wherein the capping layer is separated from the first photodiode by the first oxide layer; forming a second oxide layer over the capping layer; and etching the second oxide layer to define a second trench over the first trench.
 19. The method of claim 18, wherein etching the second oxide layer comprises exposing a first portion of the capping layer.
 20. The method of claim 19, comprising forming a color filler material in the second trench, wherein the color filler material is in contact with the first portion of the capping layer. 